For optional browning, heat 1 tablespoon oil in large nonstick skillet over medium heat until hot. Brown beef roast on all sides.
Place onion and garlic in 3-1/2 to 5 quart slow cooker; place roast on top. Cover and cook on LOW 9 to 10 hours or on HIGH 5 to 6 hours or until roast is fork-tender.
Remove roast from slow cooker. Skim fat from cooking liquid, if necessary and reserve 1 cup onion mixture. Shred beef with 2 forks. Combine shredded beef and reserved onion mixture. Season with salt and pepper, as desired. Continue as directed in Recipe Variations below, as desired.
Recipe Variations: